I read a short story around 1989 in which a man somewhere in Europe (London/Paris maybe) sent a pocket watch somewhere (in time) and it came back a few minutes later rusted. The man decided to send himself wherever the watch went (I can't remember if the man knew this involved time-travel or not). Anyway, he ended up in a jungle of some type and ended up either befriending a caveman or the caveman took pity on him and taught him how to survive. I remember there was also a cave woman that came into the picture at some point as a love interest. The man ends up being in the past for months or years and just as he's accepted this as his new life he is somehow brought back to the future where only a few minutes or hours have passed and he realizes that is why the watch looked rusty after only being gone for a few time.
I've looked for this story for years and can't find anything or anyone that knows about it. I remember that it was in a book that had a few other time-travel stories and was probably published between the 50's and 70's. I think the book included The Time Machine, in-turn which is what led me to this other story but, I've been unable to find it via that route either.
Any help would be appreciated and would finally end a 25+ year quest to find it again. Thanks for any help.